1. Field of the Invention
The present invention pertains to an exhaust port assembly for use in a pressure support system and, in particular, to a self-directing exhaust port assembly with enhanced noise reduction and gas diffusion capabilities. The present invention also pertains to a pressure support system which employs such a self-directing exhaust port assembly and a method of providing a regimen of respiratory therapy to a patient.
2. Description of the Related Art
It is well known to treat a patient with a non-invasive positive pressure support therapy, in which a flow of breathing gas is delivered to the airway of a patient at a pressure greater than the ambient atmospheric pressure. For example, it is known to use a continuous positive airway pressure (CPAP) device to supply a constant positive pressure to the airway of a patient throughout the patient's respiratory cycle to treat obstructive sleep apnea (OSA), as well as other cardio-pulmonary disorders, such at congestive heart failure (CHF) and cheynes-stokes respiration (CSR). Examples of such CPAP devices include the REMstar® family of CPAP devices manufactured by Respironics, Inc. of Murrysville, Pa.
A “bi-level” non-invasive positive pressure therapy, in which the pressure of gas delivered to the patient varies with the patient's breathing cycle, is also known. For example, a “bi-level” pressure support system provides an inspiratory positive airway pressure (IPAP) that is greater than an expiratory positive airway pressure (EPAP). IPAP refers to the pressure of the flow of gas delivered to the patient's airway during the inspiratory phase; whereas EPAP refers to the pressure of the flow of gas delivered to the patient's airway during the expiratory phase. Such a bi-level mode of pressure support is provided by the BiPAP® family of devices manufactured and distributed by Respironics, Inc. and is taught, for example, in U.S. Pat. No. 5,148,802 to Sanders et al., U.S. Pat. No. 5,313,937 to Zdrojkowski et al., U.S. Pat. No. 5,433,193 to Sanders et al., U.S. Pat. No. 5,632,269 to Zdrojkowski et al., U.S. Pat. No. 5,803,065 to Zdrojkowski et al., and U.S. Pat. No. 6,029,664 to Zdrojkowski et al., the contents of each of which are incorporated herein by reference.
Auto-titration positive pressure therapy is also known. With auto-titration positive pressure therapy, the pressure of the flow of breathing gas provided to the patient changes based on the detected conditions of the patient, such as whether the patient is snoring or experiencing an apnea, hypopnea, or upper airway resistance. An example of a device that adjusts the pressure delivered to the patient based on whether or not the patient is snoring is the Virtuoso® CPAP family of devices manufactured and distributed by Respironics, Inc. This auto-titration pressure support mode is taught, for example, in U.S. Pat. Nos. 5,203,343; 5,458,137 and 6,087,747 all to Axe et al., the contents of which are incorporated herein by reference.
A further example of an auto-titration pressure support device that actively tests the patient's airway to determine whether obstruction, complete or partial, could occur and adjusts the pressure output to avoid this result is the Tranquility® Auto CPAP device, also manufactured by Respironics, Inc. This auto-titration pressure support mode is taught in U.S. Pat. No. 5,645,053 to Remmers et al., the content of which is also incorporated herein by reference.
Other modes of providing positive pressure support to a patient are known. For example, a proportional assist ventilation (PAV®) mode of pressure support provides a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing effort to increase the comfort to the patient. U.S. Pat. Nos. 5,044,362 and 5,107,830 both to Younes, the contents of which are incorporated herein by reference, teach a pressure support device capable of operating in a PAV® mode. Proportional positive airway pressure (PPAP) devices deliver breathing gas to the patient based on the flow generated by the patient. U.S. Pat. Nos. 5,535,738; 5,794,615; and 6,105,573 all to Estes et al., the contents of each of which are incorporated herein by reference, teach a pressure support device capable of operating in a PPAP mode.
For purposes of the present invention, the phases “pressure support device”, “pressure generating device”, and/or “pressure generator” (used interchangeable herein) refer to any medical device adapted for delivering a flow of breathing gas to the airway of a patient, including a ventilator, CPAP, PAV®, PPAP, or bi-level pressure support device. The phrases “pressure support system” and/or “positive pressure support system” (used interchangeable herein) include any arrangement or method employing a pressure support device and adapted for delivering a flow of breathing gas to the airway of a patient.
In a conventional pressure support system, a flexible conduit couples the pressure support device to a patient interface device. The flexible conduit forms part of what is typically referred to as a “patient circuit” which carries the flow of breathing gas from the pressure support device to patient interface device. The patient interface device connects the patient circuit with the airway of the patient so that the flow of breathing gas is delivered to the patient's airway. Examples of patient interface devices include a nasal mask, nasal and oral mask, full face mask, nasal cannula, oral mouthpiece, tracheal tube, endotracheal tube, or hood.
In a non-invasive pressure support system, i.e., a system that remains outside the patient, a single-limb patient circuit is typically used to communicate the flow of breathing gas to the airway of the patient. An exhaust port (also referred to as an exhalation vent, exhalation port, and/or exhaust vent) is provided in the patient circuit and/or the patient interface device to allow exhaust gas, such as the exhaled gas from the patient, to vent to atmosphere.
A variety of exhalation ports are known for venting gas from a single-limb patient circuit. For example, U.S. Pat. No. Re. 35,339 to Rappoport discloses a CPAP pressure support system wherein a few exhaust ports are provided directly on the patient interface device, i.e., in the wall of the mask. However, this exhaust port configuration results in a relatively direct stream of exhaust gas being directed from the mask or patient circuit. Direct streaming of the flow of exhaust gas is undesirable, because a typical CPAP system is intended to be used while the patient is asleep. Sleep for the patient or the patient's bed partner is disturbed if a stream of gas is directed at the patient or at the patient's bed partner.
The exhaust port assembly described in published PCT Application No. WO 98/34665 to Kwok is directed to minimizing the noise associated with the leakage of exhaust gas. This is allegedly accomplished by providing an elastomeric ring around the perimeter of the exhaust port. This exhaust port configuration, however, does not solve the problem of preventing a generally direct or concentrated stream of gas from being directed from the mask onto the patient or the patient's sleep partner.
U.S. Pat. No. 5,937,851 to Serowski et al., U.S. Pat. No. 6,112,745 to Lang, and published PCT Application No. WO 00/78381 to Gunaratnam et al. all disclose exhalation ports for a positive pressure support system. Each of the exhalation ports taught by these references attempts to solve the problem of preventing a stream of gas from being directed onto the patient or onto the patient's bed partner by controlling the direction of the flow of exhaust gas. For example, each of these references teaches directing the flow of exhaust gas back along the patient circuit rather than directly outward away from the patient. However, the relative direction of the stream of gas flow changes each time the patient assumes a new sleeping position, and depending on the positioning of the patient circuit, the stream of concentrated gas may be directed onto the patient or the patient's sleep partner.
Accordingly, a need exists for an apparatus and method for providing an improved exhaust port which is adapted to direct the discharge direction of a flow of exhaust gas away from the patient and/or the patient's sleep partner regardless of the patient's position, and which overcomes these and other problems associated with known systems.